DESCRIPTION: Single-cell studies are essential for biochemical characterization of heterogeneous cell behaviors. However, studying direct correlation between cell input (transfection) and output (biochemical analysis) is still challenging due to lack of high throughpu methodologies with cell selectivity and high enough sensitivity. The tool proposed here is a microwell device that will allow temporal sampling and analysis of internal biomolecules, with the additional functionality of activating cells by delivering genes, drugs, or other molecules when appropriate for the biological problem. This tool would enable fundamental studies of biological variability, input- output relationships that control mechanistic pathways, and with multiplexed automation, could serve as a drug screening platform. The major innovations of the proposed device include (1) isolation of 1,000 individual single cells in a microwell array, (2) long-term cell culture on a micro device, (3) temporal transfection and extraction of biomolecules from a target cell in a minimally invasive manner, (4) highly sensitive detection of bio samples from cell cytosol, and (5) (in Phase II) automated operation and data acquisition. To achieve the highly innovative features, the proposed micro device incorporates a PDMS-based microwell array with integrated microfluidic channels, microelectrodes, and an antibody microarray.